We propose to use a unique mouse model to investigate the immunobiologic parameters regulating the development of matastases. The basis for these studies is a metastatic tumor, MDAY-D2, developed in DBA/2 mice. High (HMV-D2) and low (LMV-D2) metastatic variants of this tumor have been isolated. HMV-D2 metastasizes at a consistent and predictable rate from subcutaneous and intradermal sites to most major visceral organs. LMV-D2 metastasizes much later, if at all. The availability of high and low metastatic variants of this tumor permits a comparative analysis of differences between LMV-D2 and HMV-D2. Differences in biologic (growth kinetics, cell invasiveness) and immunologic (antigenicity, suppressor cell regulation) factors will be analyzed to assess their importance for the dissemination and survival of tumor cells.